Mr. Musk, a megadonor, had flummoxed some Trump advisers by previously declining to write a “super max” check directly to the former president’s campaign.

Musk, the richest man in the world with a net worth of $242 billion, according to Forbes, has pledged to give away $1 million a day to voters for signing his political action committee's petition backing the Constitution, a pledge experts say raises legal questions.